Thrupny — Concept & Prototype Plan

1. Executive summary

Thrupny is a three-wheeled, front-wheel-ridden cargo bike inspired by the penny‑farthing. A single large front wheel (≥1.0 m diameter) carries the rider and primary drive pedals that rotate around the wheel center. Two large rear wheels, set approximately 1 m apart, provide lateral stability and house an assisted electric drive and braking system. The vehicle targets urban tradespeople and commuters who need a stable, energy-efficient, non‑polluting cargo vehicle.

Key promises:

• High rider visibility (rider seated above a large front wheel) for safety in urban traffic.

• Large vertical cargo box (up to 1 m wide × 1 m deep × ~2 m high) behind the rider.

• Variable internal orbital/planetary gearing inside the front wheel offering selectable mechanical advantage (e.g. 4× torque mode for starting/uphill; 4× speed mode for cruising).

• Assisted electric drive and regenerative/emergency braking in the two rear wheels.

• Optional lightweight canopy with solar cells to top up battery for assistance.

2. Basic geometry & kinematics

• Front wheel diameter (baseline): 1.0 m → circumference = π × D = 3.1416 m per wheel rotation.

• Forward distance per rider crank revolution (direct 1:1): 3.1416 m.

• Speed examples (wheel circumference × wheel RPM): if rider cadence = 60 rpm and drivetrain is 1:1, forward speed = 11.31 km/h. (If cadence = 80 rpm → 15.08 km/h.)

Selectable internal gearbox modes (interpretation & effect):

• Direct (1:1): one pedal revolution = one wheel revolution.

• Ease/starting mode (torque ×4): gearbox reduces wheel RPM to 0.25× per pedal rev but multiplies torque at the wheel by ≈4×. With a 60 rpm pedal cadence the wheel rpm would be 15 rpm → speed ≈ 2.83 km/h (useful for starting or steep climbs).

• High-speed mode (speed ×4): gearbox gives 4× wheel rpm per pedal revolution; at 60 rpm pedal cadence wheel rpm = 240 rpm → theoretical speed ≈ 45.2 km/h (practically limited by safety and legal speed limits).

 

Note: the gearbox modes described are design options. Exact ratios, losses, and ergonomics should be verified in prototype testing and FEA/kinematic simulation.

3. Conceptual layout & components

Frame & chassis

• Long, rigid steel or chromoly front fork/frame to support a 1 m+ wheel and carry rider weight directly above axle.

• Rear subframe to hold twin rear wheels about 1.0 m track width for cargo bay and stability.

• Mounting points for cargo box (modular), canopy, battery pack, motor controllers, and brakes.

Front wheel & drive

• Oversized rim (1 m diameter) and heavy-duty spokes or composite rim.

• Inner-hub planetary gearbox (sealed) that accepts pedal input mounted concentric to the wheel axle.

• Pedal assembly: radial pedal ring (like penny‑farthing style) with torque/force sensors (strain gauges or load cells) to control pedelec assist.

Rear wheels & drivetrain

• Two independent rear hub motors (geared or direct) sized to supply assistance and emergency braking.

• Integrated regenerative braking and mechanical disc brakes for redundancy. Emergency braking controlled by electronics to apply both rear braking and a parking brake.

Electronics & battery

• Battery sized for expected assist: baseline estimate 250–750 Wh depending on legal class and desired assist range.

• Motor controllers with selectable assist maps, torque-sensor input, and safety cutoffs.

• CAN bus or lightweight wiring harness, waterproof connectors, and e-bike class-compliant cutoffs.

Cargo bay

• Modular box: 1.0 m width × 1.0 m depth × up to 2.0 m height option.

• Lightweight panels (aluminium frame with composite/ABS skins) or textile fold-out for camper variant.

Safety & ergonomics

• Rider harness/seat with a low center-of-mass option to reduce tipping risk.

• Optional roll cage or partial enclosure for parent/camper variants.

• Full LED lighting, reflective panels, horn, mirrors, and possible small windshield.

4. Preliminary materials & manufacturing notes

• Frame: Chromoly steel (e.g., 4130) or 6061/7005 aluminium with gussets. Steel easier for low-volume prototyping; aluminium for lighter production versions.

• Wheels: Custom rim (aluminium alloy or composite) sized to 1 m diameter; heavy-duty hub to accommodate internal gearbox and rider load.

• Gearbox: Custom planetary gearset, hardened steel or sintered steel planets, sealed lubrication.

• Cargo box: Welding or bolted aluminium frame with composite panels; or modular polymer shells.

5. Costs — order of magnitude estimates (prototype & small batch)

 

These are preliminary ballpark ranges to budget planning and early outreach to suppliers. Exact quotes will vary by region, spec, and supplier.

One-off prototype (hand-built, single unit)

• Custom large front wheel (rim + hub + spokes + labour): £500 – £2,000 (highly variable depending on composite rim choice or heavy-duty custom build).

• Custom planetary gearbox/hub engineering + parts (design + prototype machining): £1,500 – £6,000 (off-the-shelf small planetary parts cost little, but a sealed custom torque-capable wheel gearbox with durability testing raises cost).

• Frame & welding/fabrication (single prototype): £800 – £3,000.

• Rear hub motors and controllers (two): £200 – £1,200 (depending on power and quality per motor).

• Battery pack 250–750 Wh with BMS: £150 – £800.

• Electronics, sensors, brakes, and finishing: £300 – £1,200.

• CAD, engineering, and FEA simulation (outsourced / consultancy): £1,500 – £6,000.

Estimated total for one working prototype: roughly £5,000 – £20,000.

Small batch (10–200 units) manufacturing considerations

• Tooling and jigs for frame and cargo box: £5,000 – £30,000 depending on complexity.

• Per-unit manufacture cost (frame, wheels, drivetrain, battery, electronics, assembly): £1,200 – £4,500 per unit (scale and component sourcing will push this down as quantities grow).

6. Key technical risks & mitigations

1. High centre of gravity (CG) and rollover risk

• Risk: Rider sits above a large wheel; CG could be high, increasing tip-over risk (especially during sudden maneuvers or side winds).

• Mitigations: lower rider seat as much as possible; add ballast or position heavy components (battery) low and central; widen rear track; active stability control using differential rear-wheel torque; optional roll-bar.

2. Braking & stopping distance

• Risk: High-mounted rider increases moment during braking; single front wheel braking is risky.

• Mitigations: primary mechanical braking on both rear wheels (hydraulic discs), regenerative braking, emergency deployable parking brake on front axle, limit assisted top speed, electronic ABS-style logic for rear wheels.

3. Structural loads on oversized wheel

• Risk: 1 m wheel under rider + cargo loads needs very sturdy rim/hub and spoke pattern.

• Mitigations: use high-spoke-count hubs, consider composite or box-section rim, FEA validation, heavy-duty bearings and axle assembly.

4. Gearbox durability & maintenance

• Risk: Planetary gear inside wheel will face high torque cycles and wear.

• Mitigations: robust materials, sealed lubrication, easy-replacement planet carrier, field-serviceable module.

5. Legal & classification risk (e‑assist)

• Risk: If electric assistance exceeds local regulatory limits (power or speed), the vehicle might be classified as a motor vehicle requiring registration, insurance, and license.

• Mitigations: design an assist-limited version that meets regional e-bike legal specs; provide a software lock to cap power and speed to legal levels; include clear labelling.

7. Regulatory & IP (patent) notes — suggested pathway

Regulatory (example: UK / EU context)

• If you want Thrupny to be treated as a standard pedal-assisted cycle (no registration/license), the assisted motor continuous rated power should meet local pedelec rules (e.g., 250 W and assistance cut-off at 25 km/h in many EU/UK contexts). Also make sure the product meets applicable safety standards (lighting, brakes, EN15194/CE where applicable).

Patent approach (high level)

1. Prior art check (freedom-to-operate & novelty scan): commission a patent search to check existing patents on large-wheel bicycles, planetary in-wheel gearboxes, and cargo trike arrangements.

2. File provisional/priority application: in the UK file a provisional or complete application to establish an early priority date. Budget for professional drafting to avoid narrow claims.

3. International protection (if desired): consider PCT or direct EP filings; costs rise significantly per jurisdiction.

Cost guidance (patent)

• Typical UK patent prosecution to grant for an average complexity invention is often in the range of £4,000 – £8,000 (attorney + official fees) over multiple years; a rough budget for initial UK filing and search+examination could be £2,000 – £5,000 up front, then more for prosecution and foreign filings.

 

Note: IP strategy should prioritize the novel, commercially valuable elements — likely the in-wheel gearbox integration specifically tuned for a front-ridden large wheel, novel pedal-sensor and assist-control algorithms for a direct-drive large wheel, and unique cargo/structural arrangements.

8. Branding & go-to-market suggestions

Brand name: Thrupny (good visual & story: three pennies -> Thrupny Cockney riff). Consider short logo that plays on Victorian penny‑farthing silhouette, but with a rectangular cargo box.

Product variants:

• Thrupny Trade — rugged cargo box, heavy-duty motors, focus on delivery & trades.

• Thrupny Commuter — smaller cargo, lighter weight, canopy option, emphasis on speed/comfort.

• Thrupny Parent — enclosed child seats and safety harnesses.

• Thrupny Camper — fold-out cargo to sleeping module.

Go-to-market:

• Start with a prototype & local trials with tradespeople in a single city.

• Build partnerships with urban logistics firms for pilot fleets (if keeping legal power limits).

• Attend cycle shows (e.g., CycleShow / Eurobike) to gain attention and pre-orders.

9. Next technical steps (recommended immediate actions)

1. Produce detailed CAD (solid modelling) of the frame, wheel/hub gearbox, and rear subframe. Include mounting points and cable routing. (Recommend SolidWorks/Onshape)

2. Run FEA simulations on the front fork/wheel hub and the rear subframe with representative loads (rider + cargo up to target gross vehicle mass).

3. Create a full BOM and